1. Field of the Invention
The present invention relates to a manufacturing method of a tantalum oxide film, and more particularly to a semiconductor device employing a tantalum oxide film.
2. Description of the Related Art
Heretofore, a high dielectric constant material has been required as the capacitor insulating film.
In particular, a tantalum oxide film has been considered to be a promising candidate for such a film, and has been studied widely. As the formation method of the tantalum oxide film, it is general to adopt a chemical vapor deposition (CVD) method using an organic tantalum. A tantalum oxide film formed by the CVD method is in amorphous state immediately after its formation, and includes moisture and impurities such as organic substances in the film.
Subjecting a tantalum oxide film in amorphous state to a heat treatment in an inert atmosphere at 800.degree. C. has been disclosed in Unexamined Patent Applications Laid Open, No. Sho 58-134464. However, according to the manufacturing method in this invention, the tantalum oxide film in amorphous state is crystallized while a large amount of impurities existing in the film are removed through the heat treatment at 800.degree. C. Accordingly, in this manufacturing method, a large strain is generated in the crystallized tantalum oxide film, so it gives rise to a problem that many defects occur in the film.
Moreover, in Unexamined Patent Applications Laid Open, No. Hei 10-223856 there is disclosed a crystallization treatment of a tantalum oxide film in an active oxygen atmosphere. According to the technique disclosed in this invention, first, an amorphous tantalum oxide film including crystallized tantalum oxide in some parts is formed, then by subjecting it to a low temperature heat treatment in an active oxygen atmosphere, the amorphous tantalum oxide film including crystallized tantalum oxide in some parts is converted to a crystallized tantalum oxide film. However, according to this manufacturing method many defects are generated in the crystallized tantalum oxide film, analogous to the above-mentioned invention, and results in a problem that the defects become the cause of leakage current.
Furthermore, in Unexamined Patent Applications Laid Open, No. Hei 2-283022, a method is disclosed in which after a tantalum oxide film is formed by a CVD method, a heat treatment in an ozone atmosphere at 300.degree. C. is given, then the product is subjected to a heat treatment for crystallization in an oxidizing atmosphere at 800.degree. C.
Similarly, in Unexamined Patent Applications Laid Open, No. Hei 5-102422 is disclosed a method in which after formation of a tantalum oxide film, the tantalum oxide film is thoroughly oxidized by a heat treatment in an oxygen or ozone atmosphere, then the tantalum oxide film is further subjected to a heat treatment in an oxygen atmosphere at 800.degree. C. for crystallization.
In both of the last two inventions, the amorphous tantalum oxide film is subjected to a heat treatment prior to the heat treatment for its crystallization at a high temperature. However, an oxidation treatment at a low temperature of about 300.degree. C. leaves moisture and impurities such as organic substances included in the film. Consequently, in the subsequent heat treatment of the amorphous tantalum oxide film for crystallization at a high temperature, the film is crystallized while a large amount of impurities are being removed, which gives rise to a problem that the crystallized tantalum oxide film contains many defects in it.
In addition, Unexamined Patent Applications Laid Open, No. Hei 10-229080 relates to the manufacture of an amorphous tantalum oxide film. In this invention is disclosed a method in which after the formation of a tantalum oxide film, the film is subjected to a heat treatment in an ozone atmosphere at a temperature in the range of 300 to 500.degree. C. According to this technique, an amorphous tantalum oxide film not yet crystallized, formed in the manufacturing method as described in the above, is used as an insulating film for a capacitor.
Moreover, Unexamined Patent Applications Laid Open, No. Hei 8-69998 relates to the manufacture of an amorphous tantalum oxide film. This invention discloses a method in which a tantalum oxide film is subjected to a heat treatment in a low temperature ozone or oxygen plasma at 400.degree. C. According to this technique an amorphous tantalum oxide film not yet crystallized, formed in the manufacturing methods as described in the above, is used as an insulating film for a capacitor.
Moreover, Unexamined Patent Applications Laid Open, No. Hei 6-163519 also relates to the manufacture of an amorphous tantalum oxide film. This invention discloses a method of manufacturing an amorphous tantalum oxide film by subjecting a tantalum oxide film to a heat treatment in an oxidizing atmosphere at a temperature in the range of 450 to 600.degree. C.